1. Field of the Invention
The present invention relates to an electrophotographic recording apparatus including a copying apparatus, printer or the like.
2. Description of the Related Art
Hitherto, in an electrophotographic recording apparatus, when a shortage of a developer is detected, mere resupply of the developer has been made. But, no consideration has been given to the deterioration of a developer. It has been usual that a developer is renewed only when the maintenance service is rendered to the electrophotographic recording apparatus by a specialist.
As a method of detecting a shortage of a developer, there have been a method of measuring the transmission or reflection of light, a method of measuring a change of inductance, a method of counting illuminated dots produced by a laser, LED, etc. However, according to the above methods, the detecting means becomes generally expensive. Particularly, in the electrophotographic recording apparatus using developers of a plurality of colors, when the method of measuring the transmission or reflection of light is used, since the wavelengths of the transmitted light beams differ depending on the developers of respective colors, it becomes necessary that separate detecting means are arranged for respective colors or different filters are used for respective colors. As a result, the cost of the apparatus becomes extremely high and the size thereof becomes very large. On the other hand, when using the method of measuring an inductance change, since the degree of the inductance change differs between the developers of respective colors, the measuring accuracy is deteriorated.
As an example of counting luminous dots produced by a laser, LED or the like by using a counter, JP-A-58-224363 is known and the outline thereof is shown in FIG. 5. FIG. 5 schematically shows an essential part of a conventional recording apparatus. An electrostatic latent image carrying device 21 rotates in the direction of an arrow and is charged by a charging device 22 and is exposed by an LED array device 23. The LED array device 23 is selectively driven by a driver circuit 25a so as to emit light or to stop light emission in response to an image input signal, thereby forming a latent image on the electrostatic latent image carrying device 21. A developing apparatus 24 is arranged at a position next to the LED array device 23. The developing apparatus 24 has a developer supply tank 24a. A developer is supplied by driving supply rollers 24b attached to a supply port of the tank 24a. On the other hand, the supply rollers 24b are driven by a supply roller control circuit 25b of an automatic supply amount control apparatus 25 which controls a supply amount of a developer in response to light emitting times of an LED array 23a of the LED array device 23. Upon receipt of an image input signal, the driver circuit 25a drives the LED array device 23, and, at the same time, sends the image input signal to a counter circuit 25c. The counter circuit 25c counts a total number of illuminated dots produced by the actuated LEDs and sends an output count signal to a comparator circuit 25e. The comparator circuit 25e compares the total number of illuminated dots produced by the actuated LEDs with an output of a reference counter 25d. When the comparator circuit 25e detects that the total number of illuminated dots produced by the actuated LEDs has reached a reference value, the comparator circuit 25e sends an output signal to the supply roller control circuit 25b. In response thereto, the supply roller control circuit 25b drives the supply rollers 24b for a predetermined time period, thereby causing a predetermined amount of developer to be supplied from the developer supply tank 24a into a main body of the developing apparatus 24.
As mentioned above, in the conventional electrophotographic recording apparatus which does not take the deterioration of a developer into consideration, there has been a problem such that the developer is deteriorated before a shortage of the developer occurs, thereby resulting in a reduction in the image density. On the other hand, in the conventional method of detecting a shortage of a developer, an expensive apparatus becomes necessary. Particularly, in the case of an electrophotographic recording apparatus using developers of a plurality of colors, the apparatus becomes all the more expensive.